This is an awesome ride, one of the best days of riding I've ever done. The scenery is varied, but always stunning. The roads are a joy to ride - lots of lovely flowing corners and very little traffic.
I have 2 video on my Youtube site
Bonar to Puerto de Tarna is https://youtu.be/k4SA2YnPbOk
Ouerto de Tarner to Oseja de Sajambre is at https://youtu.be/rUeU4QJwYQs
Rode these roads last year. Mile after mile of empty winding roads. Superb riding. Will be back another year to do it again.
Try it - you will like it.